When Tony Blair leaves Number 10 on Wednesday he will be much better off than Winston Churchill was when he became an ex-prime minister in 1945 - after winning the war and losing the general election.

"My grandfather was effectively bankrupt by the end of the war," says the great man's grandson - also called Winston Churchill.

Churchill was forced to put his home, Chartwell in Kent, on the market.

"Lord Camrose, the then proprietor of the Daily Telegraph was outraged," says young Winston.

"And he corralled 10 wealthy well-wishers and they each ponied up the princely sum of £5,000.

"So for £55,000 - which was a lot of money in those days - they bought Chartwell on the understanding that my grandparents would live there until the end of their days and then it would be presented to the nation."

'Cut off'

In contrast to Churchill, Blair will receive a severance package from the state worth some £300,000 a year.

Thanks to some astute lobbying by other ex-PMs, Blair will get a car, a police driver and round-the-clock special branch protection.

He will also receive an immediate prime-ministerial pension of almost £64,000 a year as well as a further £84,000 to run his office - on top of what he makes as an MP.

But how will Blair cope with life in the ex-prime ministers' club, after what his predecessor John Major describes as the longest farewell tour since Dame Nelly Melba?

Sir Winston Churchill was effectively bankrupt by the end of the war

One of Blair's closest advisers inside Number 10 told me: "Tony still doesn't know what is going to hit him.

"The thing he will miss most of all is being cut off from top-grade information.

"He will no longer receive secret intelligence reports and papers and briefings which tell him what is really going on - both in Britain and the rest of the world."

When I put this to John Major - a rueful smile of recognition came over his face.

He produced an answer worthy of Donald Rumsfeld: "People ask you questions and you're about to answer and you think to yourself, 'hang on, I'm about to express an opinion on this and I haven't seen the papers. I don't know what it is that the prime minister knows that I no longer know'.

"So here am I about to say that I think he should have handled this differently, but he may know something that I once would have known that nobody else knows."

'Disorientating experience'

Blair will also face the practical problems of adapting to the loss of the life-support system provided by Number 10.

"When you stop being prime minister it's a very disorienting experience, because you go in such a short period of time from having everything arranged for you to being on your own," says Lord Powell, who was Margaret Thatcher's right-hand man for seven years when she was prime minister.

You are very ex as an ex-prime minister

Former Tory cabinet minister Ken Clarke

"You don't have an up-to-date telephone book of your own because of course Number 10 had all your telephone numbers. Code numbers have probably changed since you came in.

"I remember being rung up by Margaret Thatcher a week or two after she left Number 10 and being told on a Sunday she had a plumbing problem. And I said 'oh dear, better get a plumber in'. And a long silence. 'How do I do that?' 'Well', I said, 'try the Yellow Pages'. And that's the way we had to go. I ended up ringing the plumber in the Yellow Pages."

The biggest question of all is how to fill the suddenly empty days.

The former Tory cabinet minister, Ken Clarke, who as an MP since 1970 has watched five prime ministers come and go says: "Like a departing captain of industry, Tony will want the next big job in the career.

"In his case I think it will be trying to govern the world and advise all the other political leaders how to run things. And he'll find that difficult, because you are very ex as an ex-prime minister."

Baroness Thatcher was not used to dealing with mundane matters

Blair's meeting with the Pope on Saturday is one key to what he plans to do.

According to one of Blair's closest advisers: "Tony is obsessed with the idea of becoming a roving envoy who would seek to reconcile the Abrahamic religions of Christianity, Judaism and Islam."

Blair sought Papal endorsement for his plans to set up an inter-faith foundation - headed by himself.

And there are also strong hopes in the White House of Blair becoming a Middle East peace negotiator on behalf of the West.

Ken Clarke scoffs at these ideas: "Not that Tony would ask for my advice, but if he did I would say, 'forget about reconciling the faiths. You have disqualified yourself from that in a very big way'."

Memoirs goldmine

Blair's former press secretary Alastair Campbell is unsurprisingly more sanguine.

"There are all sorts of things Tony will do in the future," he says.

"He is 54 - while Gladstone and Churchill were in their 80s when they left office. And if you look at someone like Bill Clinton and Al Gore and you see what they have achieved since leaving office - Tony's going to want some of that: to still be involved and focus on the big international stuff - like climate change and Africa."

An ex-prime minister's a rather unusual fish in politics

Former prime minister John Major

But Blair is also sitting on a goldmine - his memoirs. Campbell has long described his own diaries as his pension. Blair's will be worth many times more.

I asked Campbell's literary agent, Ed Victor, the New Yorker who's now the top London literary agent to the superstars, how much he thought Blair would get.

"£5m - plus or minus," replied Victor.

"And he should sell his memoirs immediately he steps down. Ronald Reagan did the deal the day after he left office, and that was very smart. Thatcher waited and I think she got less money as a result."

Blair will also have to decide on whether to stay involved in domestic politics or whether he will sign a peace treaty with Gordon Brown.

"An ex-prime minister's a rather unusual fish in politics," says John Major.

"If they say nothing, what are they doing there? If they say something, there's every chance it will be construed as an oblique attack on your successor. So it is extremely difficult to have a role that isn't capable of severe misinterpretation."

I think Tony Blair would make a minimum of $150,000 (£75,000) per lecture in America

One sure way that Blair can make big bucks outside politics is by following his wife's footsteps on the American lecture circuit.

Although the rapture that once greeted him after 9/11 has waned, Blair remains the most popular and recognisable British public figure there since Lady Thatcher. He would wow US lecture audiences.

"And the lecture circuit has another purpose for you as an ex-prime minister. When you have been used to public adulation, at least appearing before wildly enthusiastic audiences of hundreds of Americans in Tuscaloosa or elsewhere, still has a nice role in your life.

"It makes you think you are still admired and wanted - and psychologically it's a great compensation for the loss of office."

"I think Tony Blair would make a minimum of $150,000 (£75,000) per lecture in America: all expenses paid, flown there first class, put up in a nice suite," says Ed Victor.

"If he does 10 a year - say one a month - he will be making huge, huge money."

Finding happiness

But can all the money in the world make up for the loss of the most political drug of all - power?

Alastair Campbell says Blair will focus on the "big international stuff"

"I don't know whether you can be happy after being prime minister, but I can tell you that I don't believe Margaret Thatcher has not had a happy day in her life since she ceased being prime minister," says Charles Powell.

It may take you a very long time to adjust fully to no longer being the most powerful person in the land.

For the one thing all members of the ex-prime ministers' club have in common is that they have lost the most exciting job that they will ever have.

Ken Clarke sums it up: "I think almost all of them, if you said that, by some amazing miracle, you could go back tomorrow and you could be prime minister again and take on all that hassle, and all that strain, and all that criticism, and all those crises, they'd all have jumped at it and gone straight back straight away."

How to be ex-Prime Minister, Michael Cockerell's TV documentary, will be shown on BBC Four on Sunday at 2100BST.